For example, burmister presented analytical solutions for both a twolayered pavement burmister 1943 and a. Implementation of a user material routine in 3dfe codes for viscoelastic modeling and simulation of highway and airport pavements w. It will be assumed that the materials are isotropic, homogeneous and linear elastic. Mechanisticempirical me pavement design procedures are composed of a reliable response model to estimate the state of stress in the pavement and distress models in order to predict the different types of pavement distresses due to the prevailing traffic and environmental conditions. On a certain method of selection of domain for finite. Apr 19, 2016 mechanistic design procedure are based on the assumption that a pavement can be modeled as multi layered elastic or visco elastic structure on an elastic or visco elastic foundation. Surface loading of a multilayered viscoelastic pavement. Department of transportation federal highway administration. Thus based on correspondence principle in the theory of linear viscoelaticity we can. While maximum stress or umiting strain or deflection theories of failure have frequentiy been applied as design criteria for flexible pavements, it is believed that these theories are inadequate for application to viscoelastic flexible pavements. South african mechanistic design method samdm hechter. It is a true complex number as it contains both a real and imaginary component of the modulus and is normally identified by e or g. Development of design tool for nigerian cbr design of.
A layered elastic model can compute stresses, strains and deflections at any point in a pavement structure resulting from the application of a surface load. The pavement system model is multilayered elastic using multiple wheel loads up to 20. In this study, predictions of fullscale micromechanical mm finite element fe models, developed from xray computed tomography images of asphalt concrete samples that were sawn from the accelerated pavement test sections, were used to evaluate the accuracy of layered elastic theory let models that are used in pavement design today. Viscoelastic response modelling of a pavement under moving. Viscous materials, like water, resist shear flow and strain linearly with time when a stress is applied. Prediction of viscoelastic pavement responses under moving. Figure 43 illustrates this by showing schematically the strain response to a particular stress history. On the other hand, the design of rigid pavement is by plate theory and hence the wheel load on both sides of axle need to be considered. The elastic theory, which is the most popu lar method to characterize the constitutive behavior of pavement materials, grossly underpredicts pavement responses to vehicular. The term viscous implies that they deform slowly when exposed to an external force. Lecture notes ct 4860 structural pavement design design of.
Note that when the stress is removed the strain also returns to zero. Westergaard s theory and assumptions, stresses due to curling, stresses. Viscoelastic response modelling of a pavement under moving load. An example of design without soil strength test is by using hrb soil classification system, in which soils are grouped from a1 to a7 and a group index is added to differentiate soils within each group. Chatti and yun 1996 have developed the sapsim program which represents the pavement as a series of horizontal elements sublayers and a lows. Predictive design procedures, vesys user manual, report no. Highway and airport pavement design methods and analysis are based on extrapolations of the. In the flexible road pavement design a mechanistic model of a multilayered halfspace with linear elastic or viscoelastic layers is usually used for the pavement analysis. Pavement design tries to prevent the major distress such as permanent. Viscoelastic materials, as their name suggests, combine two different properties. Several computer programs have been developed for the design of pavements. Influence of asphalt viscoelastic properties on flexible pavement performance article pdf available in the baltic journal of road and bridge engineering 114. Since the early 1960s, pavement engineers have gone from empirical to mechanistic.
Some pavement design procedures recommend that the subgrade moduli determined from fwd tests, based on linear elastic theory, be divided by a factor of 2 to 3. I inputted the data for prony shear relaxation and william landel ferry shift function. In the general literature, however, the term, dynamic modulus, is often used to denote any type of modulus that has been determined under nonstatic load conditions. Layered elastic models assume that each pavement structural layer is homogeneous, isotropic, and linearly elastic. In the context of small strain theory, the constitutive equation for an isotropic viscoelastic material can be written as. Stateoftheart technique to evaluate fatigue damage in asphalt pavements m. Calculation of the elastic moduli by research report. A computational framework for viscoelastic analysis of. In this framework, asphalt concrete was treated in the context of linear viscoelastic continuum damage theory. The procedure is based on superposition principle and is computationally favourable, as it requires only reduced incremental problem to be solved numerically.
Within the context of small strain theory, the constitutive equation for isotropic viscoelastic material can be written as follows. Stresses and strains in flexible pavement using computer program. The analysis also enables the pavement designer to predict. Each layer is modelled as a linear viscoelastic material and the effects of. Implementation of a user material routine in 3dfe codes. Generally, the stress function of viscoelastic materials can be defined in an integral form. Viscoelastic analysis of hot mix asphalt pavement structures g.
Investigation of layered elastic theory prediction accuracy. Hotmix asphalt is a viscoelastic material that is characterized by. T o improve the accuracy of current design methods in predict. Each layer continuous linearly material is finite thickness except last layer topic 3 flexible pavement stress analysis 2. Pdf viscoelastic response solutions of multilayered. Design to limit permanent deformation is often related to vertical elastic strain at the formation level, which is conceptually invalid and, hence, a semiempirical procedure. The asphalt layer is considered either elastic or viscoelastic in each analysis. In order to fulfill design requirements, the resilient modulus becomes a goal during. This paper demonstrates the application of a generalized layered linear viscoelastic lve analysis for estimating flexible pavements structural response. Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. These models are used in analysis to predict critical pavement responses deflections, stresses and strains due to traffic loading and environmental conditions for selected trial or initial design. Bouldin a new method of analysis for mechanistic pavement design has been developed based on improved malerial characteristics. It would be more appropriate to consider the nonlinearity.
Linear, nonlinear, elastic, plastic, visco elastic all addup to serious computer power and time well beyond the scope of most pavement designs flexible pavement. The dynamic modulus protocol defines a linear viscoelastic test for. Assumption natural soil subgrade aggregate subbase course aggregate base courseasphalt concrete 11. The resilient modulus, which is based on recoverable strains measured in laboratory under repeated load, is widely considered a good estimator of the elastic modulus to be used with the elastic theory. Compared to threedimensional 3d fem, the computational efficiency of the 2. The visco 1 introduction elastic properties of asphalt play a crucial role in pavement. After that, the boussinesq model has been improved by the work of burmister 1945. In mechanisticempirical me pavement design and performance prediction. The procedure is based on the multilayered elastic theory mlet and the elastic viscoelastic correspondence principle using a numerical inverse laplace transform. Nevertheless, asphalt mixes are not simple materials. This is one of the way of explaining the stressstrain relationship of viscoelastic.
For example, the characteristic differences between the theories. In mechanistic design, adequate control of pavement layer thickness as well as material quality are ensured based on theoretical stress, strain or deflection analysis. Mechanisticempirical modelling of flexible pavement. Currently, the study of viscoelastic pavement in the context of general viscoelasticity theory is usually conducted through the. Aswin posted this 19 june 2019 hi, i am trying to perform the viscoelastic analysis of asphalt pavement.
Evaluation of the structureinduced rolling resistance srr. It has a long history and is still the most widely used model in applications today. Paul guyer is a registered civil engineer, mechanical engineer, fire protection engineer, and architect with over 35 years experience in the design of buildings and related. The response of pavement structures both to the fwd and to loading by a heavy truck wheel has been compared on several instrumented test roads ullidtz, 1973. Elastic theory methods assume that the pavement has adequate strength for the wheel load to be carried, and that the pavement surface after deflecting as a wheel of a vehicle moves over it, rebounds immediately. Attempts to develop rational methods of design for flexible pavements fall into three categories. It is shown that the stateof on classical layered elastic theory cf. Viscoelastic modelling for asphalt pavements software. In these lecture notes we will concentrate on the use of linear elastic multi layer theory for the calculation of stresses and strains in pavement structures.
Their response is time and temperature dependent 1, 7, 16. Since the design of flexible pavements is by layered theory, only the wheels on one side needed to be considered. Me design of pavements structures the erapave meppp code. Me design fem or fd analyses can be very complex with thousands of nodeselements. A nonlinear constitutive relationship for asphalt binders. Application of viscoelastic continuum damage approach to. Pdf influence of asphalt viscoelastic properties on.
Calculation of the elastic moduli of a two layer pavement system from measured surface deflections by frank h. When an elastic not elastomeric, or long range elastic material is stressed, there is an immediate and corresponding strain response. In contemporary times with the invention of computers, pavement design could be carried out using computer programs. To develop a better understandii of flexible pavement behavior it is believed that components of the pavement structure should be considered to be viscoelastic rather than elastic materials. Fatigue and rutting strain analysis of flexible pavements. The term elastic implies that, once a deforming force has been removed, the material will return to. This paper describes a domain selection for the purpose of a fe model creating of the linear elastic layered halfspace and boundary conditions on borders of that domain. This article addresses the question of whether the viscoelastic behavior of asphalt pavements, as part of the factors that impact the rolling resistance, might lead to substantially higher energy consumption of road traffic, as compared to nondissipative pavements. An empirical analysis of flexible pavement design can be done with or with out a soil strength test. In viscoelastic theory, the absolute value of the complex modulus e, by definition, is the dynamic modulus. Mechanistic pavement design t u b r a u n s c h w e i g multilayer elastic theory layered elastic model elastic model boussinesq, 1885 layers extend infinitely in the horizontal direction. Viscoelastic analysis of the elastomeric binder shear.
Viscoelastic material an overview sciencedirect topics. Burmister introduced the use of the multilayer elastic theory to analyse pavement structures. The asphalt layer is considered either elastic or viscoelastic in each analysis performed. Conventionally, the pavement is regarded as a layered elastic structure with many studies already being carried out based on the wellknown layered elastic theory. The use of the viscoelastic method with a dissipated energy criteria was compared to elastic analysis for those pavements tested. Pavement design tries to prevent the major distress such as permanent deformation rutting and fatigue cracking. Mitchell et al, 1974 have proposed theoretical pavement design procedures based on layered elastic theory, and have illustrated the procedure, or parts thereof, by means of a flow diagram.
Mlet multilayer elastic theory the elastic response of the tyre pavement interaction is estimated by a nonlinear mlet multi layer elastic theory approach giving the stresses and strains at desired locations. Elastic theory methods assume that the pavement has adequate. Analytical modelling of viscoelastic behaviour of hotmix asphalt j komba, j w maina, j k anochieboateng, and j oconnell csir built environment, building 2c, p o box 395, pretoria, 0001, south africa tel. Mar 29, 20 in this study, predictions of fullscale micromechanical mm finite element fe models, developed from xray computed tomography images of asphalt concrete samples that were sawn from the accelerated pavement test sections, were used to evaluate the accuracy of layered elastic theory let models that are used in pavement design today. Conventionally, multilayered elastic analysis is performed to obtain response of flexible pavements for design and inverse analyses, however, assuming asphalt pavement as a linear elastic material is an oversimplification of its actual behavior. Pdf viscoelastic modeling and field validation of flexible. Rigid pavements are constructed by portland cement concrete pcc and should be analyzed by plate theory instead of layer theory, assuming an elastic plate resting on viscous foundation. All this explains why the current design methods are classified as mechanistic empirical. In this research, the linear visco elastic lve behavior of the existing asphalt mixes is analyzed.
In the context of sustainable development fuel consumption, gas emission, this is a current issue for the pavement design. Results of this analysis indicated that the elastic theory grossly. Their mechanical properties are the principal cause of its visco elastic behavior. First, mm fe and let models were both calibrated using. Viscoelasticity is the study of materials which have a timedependence. The everstress 9 layered elastic analysis program from the washington state department of transportation was developed from weslea layered elastic analysis program. Pdf a computational framework for viscoelastic analysis of flexible. This paper provides a brief description of investigations to establish the viscoelastic nature of asphalt concrete, the presentation and discussion of a number of different types of test data, such as. The everstress 9 layered elastic analysis program from the washington.
Elastic materials strain when stretched and immediately return to their original state once the stress is removed. Analytical modelling of viscoelastic behaviour of hotmix. Pdf influence of asphalt viscoelastic properties on flexible. For example, the horizontal tensile strain at the bottom of the hma.
Ve visco elastic rate dependent fully recoverablecd continuum damage a continuum is a body that can be continually subdivided into infinitesimal small elements with properties being those of the bulk material. Vehiclepavement interaction, viscoelastic theory and assumptions, layered systems concepts, stress solutions for one, two and three layered systems, fundamental design concepts. Viscoelastic analysis of hot mix asphalt pavement structures. Pdf stresses and strains in flexible pavement using. Some applications of the elastic theory approach to the. The increase in modulus with distance from the load may be caused by other phenomena, such as a gradually. The french pavement design method consists in a pavement mechanistic analysis based on the burmister multilayer elastic model 1943 lcpc software alize 1982.
This theory teus us only the magnitude of stresses and. Using displacement calculation as an example, assume the timedomain result is tb. Viscoelastic analysis of the elastomeric binder shear resistance in relation to asphalt rutting. In rigid pavement, load is distributed by the slab action, and the pavement behaves like an elastic plate resting on a viscous medium figure 2.
A general quasistatic computational procedure is established to evaluate stresses and strains induced in the viscoelastic flexible pavement by moving traffic. This is important because of the visco elastic characteristics of the asphalt layers and the elastoplastic response of the subgrade. Generally, pavements are designed using multilayer elastic theory assuming that all materials are elastic, isotropic, and homogenous. Pavement analysis and design teaching and examination. Burmister extended boussinesqs theory from a single layer to a multilayer elastic model 4. For example, a dashpot and a spring in series constitute the maxwell model. Moore research report number 1236 a system analysis of pavement design and research implementation research study number 1869123 conducted in cooperation with the. Pavement is modeled as multilayered elastic or viscoelastic on elastic or viscoelastic foundation. Chatti and yun 1996 have developed the sapsim program which represents the pavement as a series of horizontal elements sublayers and a lows moving wheel loads to be accommodated. The use of elasticity theory to model pavement structures is very common.
Linear elastic layer theory as a model of displacements. The procedure is based on the multilayered elastic theory mlet and the elasticviscoelastic correspondence principle using a numerical inverse laplace transform. Pavement structural condition evaluation residual life. Flexible pavement mechanistic models pavement interactive. Investigation of layered elastic theory prediction. They are produced from the heavy residue after the distillation of fuels and lubricants. In this paper, a step in this direction is taken by considering the asphalt concrete surface course as a viscoelastic plate on an elastic foundation.
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